Use of triazine compounds as anxiolytics

ABSTRACT

A method of treating anxiety is disclosed comprising administering 3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine or a pharmaceutically acceptable acid addition salt thereof.

This application is a 371 of PCT/GB 94/00560 filed Mar. 18, 1994.

The present invention relates to the use of3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine and itspharmaceutically and veterinarily acceptable acid addition salts intherapy.

EP-A-0 021 121 describes a group of triazines, including3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine, which are active inthe treatment of disorders of the central nervous system, for examplepsychiatric and neurological disorders, and which are particularlyuseful as anticonvulsants for instance in the treatment of epilepsy.These triazines are non-depressant and are therefore advantageouscompared with depressant anti-epileptics such as phenobarbitone. EP-A-0247 892 describes 3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazineisethionate, a particularly preferred salt owing to its good solubility.

In mechanistic studies,3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine has been shown toproduce a use-dependent block of voltage-sensitive sodium channels (Langet at, 1993, J. Pharm. Exp. Therap., 266, 829; Lees, G. and Leach, M.J., 1993, Brain Res., 612, 190) and at anticonvulsant brainconcentrations to inhibit the release of excitatory. amino acids,principally glutamate (Leach, M. J. et at, 1986, Epilepsia, 27, 490-497;Zhu, S. G. and McGee, E. G., 1990, Neurosci. Lett., 112, 348-351).Glutamate functions as an important neurotransmitter in the mammaliancentral nervous system and has also been identified as having specificactions in the peripheral nervous system. The known anticonvulsanteffect of this compound has therefore been ascribed to its ability toact at voltage-sensitive sodium channels as an inhibitor of glutamaterelease.

Anxiety is a symptom associated with a wide range of clinicalconditions. Conventional anxiety management includes treatment withsedative anxiolytics, examples of which are benzodiazepines such asdiazepam(7-chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one).However, the clinical use of benzodiazepines is associated with adverseside-effects including dependence and ataxia. There is therefore acontinuing need for new agents which are effective anxiolytics.

It has now surprisingly been found that3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine and its salts areeffective in controlling anxiety. Accordingly, the present inventionprovides the use in the preparation of a medicament for the treatment ofanxiety or an anxiety disorder, of3,5-diamino-6-(2,3-dichlorophenyt)-1,2,4-triazine or a pharmaceuticallyor veterinarily acceptable acid addition salt thereof.

3,5-Diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine will hereinafter bereferred to as compound A. Compound A and its salts will be referred tocollectively as the present compounds. The present compounds arenon-toxic at prophylactically and therapeutically effective doses. Theyhave the important added advantage over benzodiazepines such as diazepamthat their use does not give rise to dependence or to behaviouralchanges such as ataxia (see Example 1 and the Comparative Example whichfollow).

Suitable acid addition salts of compound A include those formed withboth organic and inorganic acids. Such acid addition salts will normallybe pharmaceutically and veterinarily acceptable. Examples of such saltsinclude those formed with hydrochloric, sulphuric, citric, tartaric,phosphoric, lactic, pyruvic, acetic, succinic, fumaric, maleic,methanesulphonic, ethanesulphonic, oxaloacetic and isethionic acids. Thesalt with isethionic acid is preferred since it possesses particularlygood solubility.

The present compounds may be prepared by a process which comprisescyciising the compound of formula (II): ##STR1## and, if desired,converting compound A thus obtained into a pharmaceutically orveterinarily acceptable acid addition salt.

The cyclisation is typically carried out by heating the compound offormula II under reflux in an alkanol, preferably a C₁₋₄ alkanol, forexample methanol or ethanol, in the presence of a strong base, forexample potassium hydroxide. The process may, for instance, be carriedout as described in Example 1 of EP-A-0 021 121. The optional subsequentstep of converting the compound A into an acid addition salt isperformed by a conventional method, for example by treatment with theappropriate acid at ambient temperature. The salt with isethionic acidmay be prepared, for instance, as described in EP-A-0 247 892, inparticular in Example 3.

The starting compound of formula II may be prepared by the methoddescribed in U.S. Pat. No. 3,637,688.

Anxiety disorders are defined, in the Diagnostic and Statistical Manualof Mental Disorders (Third Edition - Revised, 1987, published by theAmerican Psychiatric Association, Washington, D.C., U.S.A., see pages235 to 253), as psychiatric conditions having symptoms of anxiety andavoidance behaviour as characteristic features.

Generalised anxiety disorder is a condition of which the essentialfeature is unrealistic or excessive anxiety and worry about two or morelife circumstances for six months or longer. During that time theaffected person is bothered by the concerns for more days than not. Whenthe person is anxious he or she manifests signs of motor tension,autonomic hyperactivity and vigilance and scanning.

Simple phobia is an anxiety disorder of which the essential feature is apersistent fear of a circumscribed stimulus, which may be an object orsituation, other than fear of having a panic attack (as in panicdisorder, referred to below) or of humiliation or embarrassment insocial situations (which falls under social phobia). Simple phobias maybe referred to as "specific" phobias and, in the population at large,most commonly involve animals such as dogs, snakes, insects and mice.Other simple phobias involve witnessing blood or tissue injury.(blood-injury phobia), closed spaces (claustrophobia), heights(acrophobia) or air travel. Exposure to the phobic stimulus will almostinvariably lead to an immediate anxiety response.

Panic disorder is a condition characterised by recurrent panic attacks,i.e. discrete periods of intense fear or discomfort with at least fourcharacteristic associated symptoms. The attacks usually last minutes(or, rarely, hours), are unexpected and do not, as in simple phobia,tend to occur immediately before or on exposure to a situation thatalmost always causes anxiety. The "unexpected" aspect of the attacks isan essential feature of the disorder. Panic attacks typically begin withthe sudden onset of intense apprehension or fear, and are accompanied byphysical symptoms such as shortness of breath, dizziness, faintness,choking, palpitations, trembling, sweating, shaking, nausea, numbness,hot flushes or chills, chest pain and so on. Panic disorder may beassociated with agoraphobia, in severe cases of which the personconcerned is virtually housebound.

Besides being central to anxiety disorders as such, anxiety occurs as asymptom associated with other psychiatric disorders and also withorganic clinical conditions.

In obsessive compulsive disorder (OCD, also called obsessive compulsiveneurosis), for instance, the primary symptom is recurrent obsessions orcompulsions of sufficient severity to cause distress, be time consumingor to interfere significantly with a person's normal routine orlifestyle. Anxiety is an associated feature of this disorder: anaffected person may, for example, show a phobic avoidance of situationsthat involve the cause of the obsession.

A further example of such psychiatric disorders is post-traumatic stressdisorder. The principal characteristic symptoms of this involvere-experiencing a traumatic (i.e. psychologically distressing) event,the avoidance of stimuli associated with that event, the numbing ofgeneral responsiveness, and increased arousal. The "events" concernedare outside the range of common experiences such as simple bereavement,chronic illness and marital conflict; examples include a serious threatto one's life or the life of one's children spouse or other closerelative and the witnessing of another person's death or injury in anaccident or following physical violence. Anxiety is a symptom commonlyassociated with this condition.

Other psychiatric conditions of which anxiety is an associated symptominclude schizophrenia, mood disorders and major depressive disorders.

Finally, organic clinical conditions with which anxiety symptoms may beassociated include Parkinson's disease, multiple sclerosis and otherphysically incapacitating disorders.

An animal model of anxiety which is suitable for testing potentialanxiolylic agents is the Vogel conflict (punished drinking) model inrats (Vogel, J. R. et al, 1971. Psychopharmacol., 21, 1-7). As in otheranimal models based on a conflict procedure, in the Vogel conflict modelthe suppression by punishment of the animal's desire to respond resultsin a state of conflict which can be likened to the human state ofanxiety.

Administration of drugs with anxiolytic properties will release thepunishment-suppressed responding. In this particular model this ismanifested as an increase in the number of licks (attempts to drink)during punishment when compared with a vehicle control.

The Vogel conflict test gained widespread use over the past 20 years orso and has proved to be a selective screening test for anti-anxietydrugs, with a good correlation with clinically effective anxiolytics.Furthermore, the testing of a range of psychoactive non-anxiolytic drugshas failed to produce false positives in the test (Vogel J. R. et al,ibid; Cook L. and Sepinwall, J., 1975: Behavioural analysis of theeffects and mechanisms of action of benzodiazepines, in "Mechanisms ofAction of Benzodiazepines", ed. Costa. E. and Greengard. P., New YorkRaven Press. pages 1 to 28: McCowen, T. J. et al 1983. Pharmacol.Biochem. Behav., 18, 277-279).

The present compounds are active in the Vogel conflict model, asdemonstrated in Example 1 which follows. The present compounds aretherefore anxiolytics. Accordingly, the present invention provides amethod of treating anxiety or an anxiety, disorder in a mammal, themethod comprising administering thereto a therapeutically effectiveamount of one of the present compounds. In this way anxiety can becontrolled and/or alleviated. The condition of a human being or animalcan thereby be improved.

The present compounds have utility in treating anxiety disorders, asdefined above, and also anxiety which occurs as a symptom associatedwith clinical conditions of either psychiatric or organic origin.Examples of anxiety disorders which the present compounds may be used totreat therefore include generalised anxiety disorder, simple phobia andpanic disorder. The present compounds are also useful in treatinganxiety which is associated with psychiatric conditions such asobsessive compulsive disorder, post-traumatic stress disorder,schizophrenia, mood disorders and major depressive disorders, and withorganic clinical conditions such as Parkinson's disease and multiplesclerosis.

The present compounds are non-toxic at prophylactically andtherapeutically effective doses. The orientative acute oral toxicity(LD₅₀) for compound A in mice is 250 mg/kg and in rats is 640 mg/kg.These are the dose levels at which 50% of the animals survive 10 daysafter administration of compound A.

The present compounds can be administered by a variety of routes and ina variety of dosage forms including those for oral, rectal, parenteral(such as subcutaneous, intramuscular and intravenous), epidural,intrathecal, intra-articular, topical and buccal administration.

The present compounds may be administered in any of the above dosageforms at a dose of from 1 mg/kg to 40 mg/kg per day, for example 5 mg/kgto 40 mg/kg, suitably 10 mg/kg to 30 mg/kg. For oral administration adose of 40 mg/kg is particularly suitable. The dose range for adulthuman beings will depend on a number of factors including the age,weight and condition of the patient and the administration route. Atypical dosage regimen is from 20 mg to 3200 mg per day, typically from350 mg to 1400 mg per day, preferably from 600 mg to 1070 mg per day. Itmay in some situations be advantageous, since the present compounds arelong-acting, to administer an initial dose of 70 mg to 3200 mg on thefirst day of treatment and then a lower dose of 20 mg to 1600 mg onsubsequent days (all doses expressed as the base).

The present invention further provides a composition comprising apharmaceutically or veterinarily acceptable carrier or diluent and, asan active principle, one of the present compounds. The composition canbe prepared using conventional methods and administered in apharmaceutically acceptable form.

For oral administration, fine powders or granules containing diluting,dispersing and/or surface-active agents may be presented in a draught,in water or a syrup, in capsules or sachets in the dry state, in anon-aqueous suspension wherein suspending agents may be included, or ina suspension in water or a syrup. Where desirable or necessary,flavouring, preserving, suspending, thickening or emulsifying agents canbe included. When a suspension is prepared in water according to thepresent invention at least one of such agents will be present.

Other compounds which may be included by admixture are, for example,medically inert ingredients, e.g. solid and liquid diluent, such aslactose, dextrose, saccharose, cellulose, starch or calcium phosphatefor tablets or capsules, olive oil or ethyl oleate for soft capsules andwater or vegetable oil for suspensions or emulsions; lubricating agentssuch as silica, talc, stearic acid, magnesium or calcium stearate and/orpolyethylene glycols: gelling agents such as colloidal clays: thickeningagents such as gum tragacanth or sodium alginate: binding agents such asstarches, arabic gums, gelatin, methylcellulose, carboxymethylcelluloseor polyvinylpyrrolidone; disintegrating agents such as starch, alginicacid, alginates or sodium starch glycolate; effervescing mixtures:dyestuffs; sweeteners: wetting agents such as lecithin, polysorbates orlaurylsulphates; and other therapeutically acceptable accessoryingredients, such as humectants, preservatives, buffers andantioxidants, which are known additives for such formulations.

Liquid dispersions for oral administration may be syrups, emulsions orsuspensions. The syrups may contain as carrier, for example, saccharoseor saccharose with glycerol and/or mannitol and/or sorbitol. Inparticular a syrup for diabetic patients can contain as carriers onlyproducts, for example sorbitol, which do not metabolise to glucose orwhich metabolise only a very small amount to glucose. The suspensionsand the emulsions may contain a carrier, for example a natural gum,agar, sodium alginate, pectin, methylcellulose, carboxymethylcelluloseor polyvinyl alcohol.

Suspensions or solutions for intramuscular injection may contain,together with the active compound, a pharmaceutically acceptable carriersuch as sterile water, olive oil, ethyl oleate, glycols such aspropylene glycol and, if desired, a suitable amount of lidocainehydrochloride. Solutions for intravenous injection or infusion maycontain a carrier, for example, sterile water which is generally Waterfor Injection. Preferably, however, they may take the form of a sterile,aqueous, isotonic saline solution. Alternatively, the present compoundsmay be encapsulated within liposomes.

The present compounds may also be administered in pure form unassociatedwith other additives, in which case a capsule, sachet or tablet is thepreferred dosage form.

Tablets and other forms of presentation provided in discrete unitsconveniently contain a daily dose, or an appropriate fraction thereof ofone of the present compounds. For example units may contain from 5 mg to500 mg, but more usually from 10 mg to 250 mg, of one of the presentcompounds (expressed as the base).

The invention is further illustrated in the Examples which follow.

BRIEF DESCRIPTION OF FIGURE

In the accompanying drawing:

FIG. 1 is a graph of mean number of licks (±s.e.m., y axis) per 5-minutesession for compound A isethionate at doses of 0, 10, 20 and 40 mg/kgbase equivalent in the rat model test of Example 1.

EXAMPLE 1

Testing of compound A in the Vogel conflict model of anxiety in rats

Methods & Materials

Animals

Male hooded Lister rats (Charles River), 150-200 g, were maintained ingroups of 7-10 and given food ad libitum. 24-Hours prior to the test thewater bottles were removed from the home cages.

Apparatus

The apparatus consisted of an operant conditioning chamber (Skinner box)which contained a grid floor and an externally mounted drinking bottle,the spout of which was accessible from inside the chamber. The chamberwas housed inside a ventilated sound-attenuating box. Licks at the spoutwere detected by "Drinkometer" circuitry, (Campden Instruments Ltd.,London W8 7TH, U.K.) whereby contact between the grid floor and drinkingspout completed a circuit. Experimental control was performed by a"Spider" microcomputer system (Paul Fray Ltd., Waterbeach, Cambridge CB59QZ, U.K.) which counted licks from the "Drinkometer" circuit,controlled session timers and shock delivery from a constant currentshock generator (Campden Instruments Ltd.) and produced raw dataprintouts.

Procedure

On the morning of the test day (18-20 hours water deprivation) theanimals were individually placed in the chamber and allowed a 5-minuteshock-free session in which to familiarise themselves with the drinkingspout and initiate licking (pre-test). Accumulation of 500 licksterminated the session. Rats not achieving the required 500 licks withinthe 5 minutes were not used. After a further period of water deprivation(up to the total of 24 hours) and the required drug/vehiclepretreatments, the rats were individually replaced in the chamber. Forthis second part of the test the animals were allowed 40 licks at thespout before a 5-minute session was automatically triggered by the 41stlick. During this 5-minute session, every 20th lick at the spout wasaccompanied by a small electric shock (0.075 mA for 0.5 seconds)delivered between the spout and the grid floor. The shock was alwaysavoidable, being contingent on licks from the drinking bottle, and wasterminated when contact with the spout was broken. The number of lickswas recorded.

Statistics

Statistical comparisons were made using a Mann-Whitney U-test. Thisnon-parametric test was appropriate since it is not always acceptable tomake assumptions concerning the population in these types of behaviouralexperiments. p Values of less than 0.05 were regarded as indicatingsignificant effects. Since the Mann-Whitney test ranks the raw data itrelies on ordinal scaling. In such cases it is not strictly valid toexpress the results as a mean ±standard error. However, for the purposesof clarity in expressing the results, means and standard errors havebeen used.

Compounds used

The isethionate salt of compound A was dissolved in distilled water andadministered orally, in a volume of 5 ml/kg, one hour before test.Control animals received water vehicle alone.

The results (number of licks) are shown in the following Table 1 and inthe accompanying FIG. 1.

                  TABLE 1    ______________________________________                 Dose p.o.                 (mg/kg base equivalent)                 10       20     40    ______________________________________    Compound A isethionate                   92         165    208    ______________________________________

The data are expressed as percentage of vehicle control responding[vehicle=100%]. Increases above 100% represent anxiolytic effects anddecreases represent anxiogenic effects. The highlighted figurerepresents a statistically significant (p<0.05) anxiolytic effect.

FIG. 1 shows that compound A isethionate produced a dose-relatedincrease in punished responding at 20 and 40 mg/kg, that at the latterdose being significant. Importantly, no other behavioural changes wereobserved.

COMPARATIVE EXAMPLE

Testing of reference compounds in the Vogel conflict model of anxiety inrats

Using the methods and materials described in Example 1, the followingcompounds were tested: diazepam (10 mg ampoules, Roche), knownanxiolytic, used as positive control, and the standard anticonvulsantscarbamazepine (Sigmna) and phenytoin* (Sigma). The diazepam was dilutedfrom the ampoules using distilled water and administered subcutaneously(2 ml/kg) 20 minutes before test. Carbamazepine and phenytoin weresuspended in 0.25% (w/v) aqueous celacol using a ballmill andadministered orally at 5 ml/kg, one hour before test.

* sodium salt; doses expressed as parent acid equivalent

The results (number of licks) are shown in the following Table 2.

                  TABLE 2    ______________________________________           Dose (mg/kg)    Compound 0.5    1.0      5.0  10.0   20.0 40.0    ______________________________________    Diazepam 162    296    (s.c.)    Carbamazepine            87          161    (p.o.)    Phenytoin                     121         114    (p.o.)    ______________________________________

The data are expressed as percentage of vehicle control responding[vehicle=100%]. Increases above 100% represent anxiolytic effects anddecreases represent anxiogenic effects. The highlighted figuresrepresent statistically significant (p<0.05) anxiolytic effects.

The results show that diazepam produced a dose-related increase inpunished responding (PR) at 0.5 and 1.0 mg/kg. This effect was large andsignificant. However, at 1.0 mg/kg it was accompanied by ataxia, aresult of the muscle relaxant effect which commonly occurs withbenzodiazepines.

Carbamazepine and phenytoin were tested as they have anticonvulsantproperties in common with compound A and its salts. However,carbamazepine produced no effect at 5.0 mg/kg and a non-significantincrease in PR at 20 mg/kg. Phenytoin produced no effect on PR at either10 or 40 mg/kg.

In a further series of tests, again using the methods and materialsdescribed in Example 1, the following compounds were evaluated:

    ______________________________________    standard anticonvulsants:                       carbamazepine                       ethosuximide                       phenytoin sodium                       sodium valproate    5-HT.sub.3 receptor antagonists:                       bemesetron (MDL 72222)                       ondansetron hydrochloride    ______________________________________

Bemesetron was administered in a mixture of dimethyl sulphoxide anddistilled water, the rest in 0.25% (w/v) aqueous celacol; all were givenone hour before test at 5 ml/kg.

The results (number of licks) are shown in the following Table 3; forsalts, doses are expressed as equivalent of the parent moiety.

                                      TABLE 3    __________________________________________________________________________                Dose p.o. (mg/kg)*    Compound    0.1                  0.5                    1.0                       10 20 40 80 100                                      160                                         320    __________________________________________________________________________    Carbamazepine      154                          206                             219                                309    Ethosuximide              64                                133    61                                          96    Phenytoin sodium      101                             135                                220   173    Sodium valproate          79                                108   151                                         261    Bemesetron  89  129                       156         116    Ondansetron hydrochloride                68   80                        70          87    __________________________________________________________________________     *Bemesetron and ondansetron hydrochloride doses in μg/kg

The data are expressed as percentage of vehicle control responding[vehicle=100%]. Increases above 100% represent anxiolytic effects anddecreases represent anxiogenic effects. The highlighted figuresrepresent statistically significant (p<0.05) anxiolytic effects.

The results show that only carbamazepine produced a dose-related,significant increase in punished responding.

The 5-HT₃ receptor antagonists, bemesetron and ondansetron, have beenreported to exhibit anxiolytic effects in other animal models. Theirlack of any significant anxiolytic effect in the Vogel conflict model,in contrast with compound A isethionate (Example 1), suggests that thisproperty of compound A and its salts is not mediated via the 5-HT₃receptor.

EXAMPLE 2

Pharmaceutical composition

Tablets for oral administration are formulated with the followingingredients:

    ______________________________________    Compound A        150 mg    Lactose           200 mg    Maize starch       50 mg    Polyvinylpyrrolidone                       4 mg    Magnesium stearate                       4 mg    ______________________________________

Mix the active compound with the lactose and starch and granulate with asolution of the polyvinylpyrrolidone in water. Dry the resultinggranules, mix with the magnesium stearate and compress to give tabletsof average weight 408 mg.

I claim:
 1. A method of treating anxiety or an anxiety disorder in a mammal, the method comprising administering thereto a therapeutically effective amount of a compound selected from 3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine and a pharmaceutically veterinarily acceptable acid addition salt thereof.
 2. The method according to claim 1 wherein the mammal is man.
 3. A method according to claim 1 where the acid addition salt is 3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine isethionate.
 4. A method according to claim 1 wherein the anxiety disorder is generalized anxiety disorder.
 5. A method according to claim 1 wherein the anxiety disorder is simple phobia or panic disorder.
 6. A method according to claim 1 wherein the anxiety is associated with obsessive compulsive disorder or with post-traumatic, stress disorder.
 7. A method according to claim 1 wherein the anxiety disorder is associated with schizophrenia, a mood disorder or a major depressive disorder.
 8. A method according to claim 1 (wherein the anxiety disorder is associated with an organic condition.
 9. A method according to claim 8 wherein the organic condition is Parkinson's disease or multiple sclerosis. 